The present invention concerns an autonomous system for measuring, processing, and transmitting essentially physiological parameters. It is increasingly important in the treatment of numerous illnesses and in the practice of several sports to know accurately certain physiological parameters of an individual, such as the heartbeat rate, blood pressure, blood sugar level, as well as parameters connected to the sporting activity, such as the speed or the power developed by the individual. To this end, numerous types of light sensors which are easy to attach to the wearer have been developed over recent years, ranging from simple electric contacts for taking an electrocardiogram (ECG), to complex sensors directly incorporated for example in silicon chips.
Most of these sensors provide electric signals in connection with the parameter(s) to be measured and carry numerous useful data. For example, for an electrocardiogram, there will be characteristic pulses whose frequency directly reflects the heartbeat rate. However, a deeper analysis of the shape of these pulses could provide additional information on certain malfunctions and could thus enable certain cardiac failures to be prevented.
The processing of the signals provided by the sensors presents no problem in the case where the individual can be connected to a fixed installation, for example when the person is confined to bed, or is only connected to a fixed measuring installation for a relatively short period of time. A design of this type corresponds for example to the device disclosed in patent application GB-A-2 259 772 in which detecting apparatus worn by several users transmit biological data to a central unit via radio waves. It is completely different if long term monitoring is desired and/or if the person has to maintain total mobility, while still being able to have easy access to read the desired parameters. At the present time, it is possible to make small autonomous signal processing devices capable of being attached to the individual, for example directly onto the abdomen by means of a belt or straps. It is easy to understand in the case cited above that, in order to be easily read, the means for displaying the parameters must be separated from the signal processing system. A wire connection is also delicate in that this wire may easily break when the person moves.
An interesting example of wireless connection is given by certain heartbeat rate reading systems used for training high level sportspersons. These systems comprise a belt including ECG signal sensors and a simple signal shaping device generating pulses at the heartbeat rate. These pulses are then transmitted without wire by all or nothing modulation of a radio signal to a device for receiving, processing and measuring these signals, enabling the heartbeat rate to be computed and displayed. The receiving and display device may for example be incorporated in a watch attached to the wrist, or placed on the handlebar of a bicycle, in the manner most suited to the type of use. It may then be combined with other functions, particularly time or stopwatch functions. A device of this type is for example disclosed in patent application FR-A-2 685 189. The first significant drawback of the known systems lies in the fact that the measuring is carried out at the receiving device. Thus any interference in the radio connection may introduce measuring errors and an erroneous display of the heartbeat rate. The second significant drawback is the limitation of a system of this type. In its present design it allows only the heartbeat rate to be measured, since it merely transmits pulses at this rate. However, as seen above, certain applications require a deeper analysis of the ECG signal, or even the analysis of parameters provided by other types of sensors. A final important point consists of reducing as much as possible the energy consumption, particularly as regards the receiving and display device, which is usually supplied with power by battery and must be as autonomous as possible, especially if it is also used as a watch as stated above.